It is conventional practice to install one or more breather bags in a conventional sealed type of agricultural silo. The silo, being a generally upright cylindrical structure, is typically filled with silage or other material to some level below the inside top of the silo.
The silo is typically not completely filled with silage or other material so that there exists a free space or free volume at the top of the silo above the upper surface of the silage or other material. One or more breather bags, fabricated from a flexible thermoplastic material such as polyvinylchloride, are suspended in the free space at the top of the silo. The interior of each bag is open to the outside atmosphere, through a conduit connecting the bag to the roof of the silo, so that the bag can accommodate inflowing ambient air when the pressure in the silo is reduced below ambient air pressure and so that the bag can discharge air when the pressure within the silo is greater than the ambient air pressure.
It is desired to prevent spoilage of the silage in the silo. This is accomplished by providing a substantially airtight or leaktight silo structure to prevent ambient atmosphere from contacting the silage. However, a substantially airtight silo structure must be able to withstand changes in internal pressure. Specifically, any small amount of air remaining in the silo and the gases generated by the silage will expand or contract with changes in ambient temperature. When the temperature increases, the expanding gases cause an increase in internal silo pressure. Conversely, when the temperature decreases, the contracting gases cause a decrease in pressure.
The silo must therefore be designed to withstand a pressure increase which could cause the silo to explode. Similarly, the silo must be designed to withstand a pressure decrease which could result in an implosion of the silo.
The pressure changes are minimized by the use of the breather bag. Specifically, when the temperature decreases and the pressure tends to decrease within the silo, the higher pressure ambient air fills and inflates the breather bag within the silo so that the pressure within the silo does not significantly decrease. Conversely, when the temperature increases and the pressure within the silo tends to increase, the breather bag partially or completely collapses and the air is expelled therefrom. Thus, the pressure within the silo around the bag does not increase significantly.
One conventional type of silo breather bag that is widely used in the United States of America today has a generally partial torous or weiner-like configuration and is hung from the top of the silo from hooks arranged in an approximately semi-circular array around the top of the silo. Typically, two such bags are suspended in a silo end-to-end (but not interconnected) whereby the two separate bags together can be said to form a generally toroidal shape. Depending upon the bag length and upon the silo size, only one bag may be used in some cases, while in other cases, more than two bags may be used.
The silo breather bag must be designed to withstand the stresses imposed by the support system in addition to the stresses imposed by inflation. These weiner-like silo breather bags are typically fabricated from a plurality of pieces or panels of flexible polyvinylchloride material which are joined together with a sealed seam along overlapping edges. Typically the seams are effected with a heat seal or with a high frequency welding process. Of course, it is desired to fabricate a breather bag that will maintain its integrity and not fail at or adjacent such seams.
Although a breather bag may function satisfactorily during a normal use, it has been found that breather bags do fail in the field on occasion, as by rupturing or tearing, and such failures may be attributable to incorrect installation, abuse during installation, and the like. These failed bags must be replaced, preferably with a bag of similar shape so that the existing support structure can be used.
Further, it has been found that the ruptures or tears, when they do occur, are frequently located in the bags adjacent the panel seams. Thus, it would be desirable to provide an improved multi-panel breather bag construction that would better withstand abuse during installation and that would better withstand stresses arising from incorrect installation or from unexpected inflation pressure excursions.
With conventional breather bag construction, the seams must be properly formed along their entire length to ensure the integrity of the bag and to reduce the probability of the bag tearing or rupturing at or adjacent the seams. Consequently, it would be desirable, ceteris paribus, to provide a minimum number of seams and a minimum seam length so as to reduce the amount of seams that must be produced.
With some weiner-like breather bag configurations, there are places in the bag where three or more separate pieces or panels of material are joined together at one point. At these points an edge of each piece overlaps the edges of the other pieces.
A seam weld of three or more layers of polyvinylchloride panel material is of potentially greater concern than the overlapping seam weld of just two pieces of the material. Greater care must be taken when making a weld of three or more overlapping pieces to ensure that the weld satisfactorily joins all of the pieces. Further, owing to the greater bulk of material at the weld, it is believed that a weld of three or more pieces provides a more significant stress riser or discontinuity in the composite structure at or adjacent the welded seam than does a weld of just two pieces.
It has been determined that bags are more likely to fail at such welds of three or more panels than at, or along, welds of just two overlapping panels. Consequently, it would be desirable to provide a breather bag of improved construction in which the number of welds of three or more pieces of material is reduced to a minimum.
Although weiner-like or partial torous-shaped breather bags are preferably fabricated from a plurality of separate panels or pieces of polyvinylchloride material to more accurately and easily provide the desired inflated shape, the fabrication and assembly of many separate pieces or panels necessarily involves a substantial amount of labor and time. Accordingly, it would be desirable to provide a breather bag having a weiner-like configuration with a small number of separate panels so as to reduce the labor and time required for the fabrication of such a bag.
Further, it would be desirable to provide a breather bag in which the ratio of the edge length of each panel to the area of that panel is as small as possible. Additionally, it would be desirable to fabricate the panels in planar shapes that are not too complex and which require no, or relatively few, seams within each separate panel. This would reduce the labor and time required to fabricate each panel.